Silicon photonics is one of the most promising solutions to achieve low cost CMOS-compatible optical integrated circuits (OICs) and nearly all the components of silicon photonics interconnections have been individually demonstrated. However, a proper way to monolithically integrate the robust and low-powered lasers into silicon photonics platform is still under investigation. Specifically, current approaches are highly inefficient and not robust against temperature variations (requires T<40-80° C. for operation).
Mode-locked lasers have the ability to generate ultrashort pulses from femtosecond to sub picosecond which can be used for optical clock signal generation, OTDM, WDM, high speed electro-optic sampling systems and so on. In addition to using the bulky Ti:sapphire laser or other vibronic laser to generate pulses light, semiconductor mode-locked lasers (MLLs) have been demonstrated in near infrared and hybrid quantum well MLLs has recently been demonstrated, which provide opportunities for photonic integrations.
InAs quantum dot (QD) lasers are attractive candidates for photonic integration due to their capability for high temperature operation. Recently, InAs QD lasers were monolithically grown on silicon substrates. These novel direct growth technologies need to apply either 4-6° off-cut or pre-patterned silicon substrates first and then grow thick buffer layers to eliminate the threading dislocations (TDs) between Si and GaAs, both of which limit CMOS compatibility. Up to date, ultrafast, high repetition rate, low-jitter, temperature insensitive quantum dot mode-locked lasers (QD-MLLs) have been successfully proved. Currently, only quantum well mode-locked lasers (QW-MLLs) have been demonstrated on silicon by evanescent coupling method which may have low efficiency and thermal issues for photonics integration.